1. Field of the Invention
The present invention relates to a developing unit, a process cartridge, and a developing cartridge for developing images using developing agent.
2. Description of Related Art
A conventional image forming device includes a known developing unit that develops electrostatic latent images into visible images using charged particles of toner. This type of developing unit can leek toner. The leaked toner can stain the interior of the image forming device and recording sheets, thereby degrading printing quality. The leaked toner can also stain the user's hands or clothes during replacement of the developing unit.
One such developing unit with this problem includes a developing roller and a layer thickness regulating blade. The developing roller transports toner on its surface, and the layer thickness regulating blade regulates the toner on the surface of the developing roller to a thin layer. The layer thickness regulating blade includes a stainless steel plate spring and a resin or rubber pressing member, both formed to the same length in their lengthwise direction. Non magnetic single component developing agent is used as toner. The toner easily leaks from around the edges of the developing roller as the developing roller rotates.
Conventionally. various configurations have been provided inside the developing unit in order to prevent toner leakage. As will be described next, side seals and slower film are examples of configuration provided for preventing toner leakage.
The side seals are formed from a urethane sponge with a Teflon.TM. felt attached thereto. The urethane sponge needs to be sufficiently soft and have a low compression set. The Teflon.TM. felt can be pressed with sufficient pressing force against the developing roller, without increasing rotational torque required for rotating the developing roller.
The lower film is usually made from urethane rubber or a polyethylene terephthalate (PET) sheet. Although the urethane rubber provides a sufficiently soft pressing force, it has insufficiently low stiffness on its own. and so needs to be pressed from behind by a sponge or other member. The PET sheet is stiffer than the urethane rubber film and so does not need to be pressed from behind by a sponge member. Therefore, the PET sheet makes assembly processes easier than does the urethane rubber film.